/*
 * Copyright (c) 2012 Lawrence Livermore National Laboratory
 *
 * SPDX-License-Identifier: GPL-2.0-only
 *
 * Author: Peter D. Barnes, Jr. <pdbarnes@llnl.gov>
 */

#ifndef HASH_MURMUR3_H
#define HASH_MURMUR3_H

#include "hash-function.h"

/**
 * @file
 * @ingroup hash
 * @brief ns3::Hash::Function::Murmur3 declaration.
 */

namespace ns3
{

namespace Hash
{

namespace Function
{

/**
 *  @ingroup hash
 *
 *  @brief Murmur3 hash function implementation
 *
 *  Adapted from http://code.google.com/p/smhasher/
 *
 *  MurmurHash3 was written by Austin Appleby, and is placed in the public
 *  domain. The author hereby disclaims copyright to this source code.

 *  Note - The x86 and x64 versions do _not_ produce the same results, as the
 *  algorithms are optimized for their respective platforms. You can still
 *  compile and run any of them on any platform, but your performance with the
 *  non-native version will be less than optimal.
 */
class Murmur3 : public Implementation
{
  public:
    /**
     * Constructor, clears internal state
     */
    Murmur3();
    /**
     * Compute 32-bit hash of a byte buffer
     *
     * Call clear () between calls to GetHash32() to reset the
     * internal state and hash each buffer separately.
     *
     * If you don't call clear() between calls to GetHash32,
     * you can hash successive buffers.  The final return value
     * will be the cumulative hash across all calls.
     *
     * @param [in] buffer pointer to the beginning of the buffer
     * @param [in] size length of the buffer, in bytes
     * @return 32-bit hash of the buffer
     */
    uint32_t GetHash32(const char* buffer, const std::size_t size) override;
    /**
     * Compute 64-bit hash of a byte buffer.
     *
     * Call clear () between calls to GetHash64() to reset the
     * internal state and hash each buffer separately.
     *
     * If you don't call clear() between calls to GetHash64,
     * you can hash successive buffers.  The final return value
     * will be the cumulative hash across all calls.
     *
     * @param [in] buffer pointer to the beginning of the buffer
     * @param [in] size length of the buffer, in bytes
     * @return 64-bit hash of the buffer
     */
    uint64_t GetHash64(const char* buffer, const std::size_t size) override;
    /**
     * Restore initial state
     */
    void clear() override;

  private:
    /**
     * Seed value
     *
     * This has to be a constant for all MPI ranks to generate
     * the same hash from the same string.
     */
    static constexpr auto SEED{0x8BADF00D}; // Ate bad food

    /**
     * Cache last hash value, and total bytes hashed (needed to finalize),
     * for incremental hashing
     */
    /**@{*/
    uint32_t m_hash32;
    std::size_t m_size32;
    /**@}*/

    /** murmur3 produces 128-bit hash and state; we use just the first 64-bits. */
    /**@{*/
    uint64_t m_hash64[2];
    std::size_t m_size64;
    /**@}*/

}; // class Murmur3

} // namespace Function

} // namespace Hash

} // namespace ns3

#endif /* HASH_MURMUR3_H */
